Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

The structure

Atomic Spectra Database

Composites science and technology

A full tungsten divertor for ITER: Physics issues and design status

With incident power densities of 5-10MW/m or higher, divertor target plates of large tokamaks are driven close to the material limits. The power handling performance is essential to their characterisation. The thermal performance of tungsten is critical to the decision as to whether to start ITER with an all tungsten divertor. In the new ITER-like Wall in JET, the divertor tiles consist of carbon-fibre composites coated with tungsten except for a specific row within the range of the outer strike point (horizontal target) where bulk tungsten is used. The multilayer coating (Mo/W) is 12-25m thick depending on the poloidal position. Ion beam tests have shown that the risk of delamination is low (<1% area) as long as the coating is maintained below 1200°C and carbidisation is negligible. The tiles are coated by combined magnetron sputtering and ion implantation (CMSII). The bulk tungsten row consists of 48 tile assemblies. Each one is made of two sets of four stacks of 24 lamellae. The stacks are aligned with the toroidal direction. To minimise the risk of fracture, the brittle tungsten is subjected by the clamping to compression forces only. The surface temperature was initially limited to 1200°C to avoid appreciable grain growth and possible thermo-mechanical fatigue (no higher temperature was recorded, by the infrared systems up to now: Tsurf<1200°C). Densities of deposited energy in the order of 2030 MJ/m were reached so far. The modelled temperature rise of the plasma-facing tungsten components shows a fair agreement with the records of thermocouples and of infrared cameras. The experimental behaviour is close to the design values in a wide range of operational parameters. Special protruding lamellae were designed to expose leading edges with a vertical step  0.3mm with the aim of deliberate melting. These future investigations are intended to support ITER since melting is the highest risk for a solid tungsten divertor.

http://www-naweb.iaea.org/napc/physics/FEC/FEC2012/papers/497_EXP524.pdf

Power Handling of the Tungsten Divertor in JET

Powder metallurgically produced tungsten fiber-reinforced tungsten composites

The consequences of tungsten (W) cracking on divertor lifetime and plasma operation are high priority issues for ITER. One actively cooled ITER-like plasma facing unit (PFU) has been pre-damaged in a High Heat Flux (HHF) facility before its installation in WEST in order to assess the damage evolution after tokamak plasma exposure. The resulting pre-damage exhibits micrometer-size crack network and high roughness on the tungsten monoblock (MB) top surface. A total of 10 MBs, equally distributed on the low and high field sides of the lower divertor, have been pre-damaged among the 35 radially aligned MBs characteristic of the WEST PFU. Subsequent plasma exposure was carried out, from the first breakdown achieved in WEST (in 2017) until the removal of the damaged PFU three years later (2020). On top of the whole WEST plasma exposure (covering C1-C4 experimental campaigns), a dedicated experiment has also been performed in the frame of the EU work program to maximize the power and energy loads on one of the damaged MBs featuring a “crack network” pattern. The MB top surface, including both “crack network” damage and “healthy” (undamaged) areas, was monitored with a high spatial resolution IR camera to detect any potential evolution of the damage pulse after pulse. This paper describes the full plasma exposure achieved in the WEST tokamak (including large number of steady-state and transient heat loading cycles), the dedicated “damaged PFU exposure” experiment together with the experimental results (heat loading on the damaged MBs). Post-mortem measurement reveals significant broadening of the cracks and new cracks in the electron beam loaded area only. 

Second plasma exposure of a pre-damaged ITER-like Plasma Facing Unit in the WEST tokamak: in-situ and post-mortem measurements

Material issues pose a significant challenge for future fusion reactors like DEMO, hence the development of advanced materials is essential for sophisticated energy systems like a future fusion reactor. When using materials in a fusion environment a highly integrated approach is required. Damage resilience, oxidation resistance during accidental air ingress as well as power exhaust are driving issues when deciding for new materials. Neutron induced effects e.g. transmutation adding to embrittlement are crucial to material performance. Here advanced materials e.g. composites allow the step towards a fusion reactor. Wf/W contributes to advanced material strength and crack resilience even with a brittle matrix. Tungsten fiber-reinforced tungsten composites (Wf/W ) utilize extrinsic toughening mechanisms and therefore overcome the intrinsic brittleness of tungsten at low temperature and its sensitivity to operational embrittlement. Wf/W has been successfully produced and tested during the last years and the focus is now put on the technological realization for the use in plasma facing components of fusion devices. In this contribution, we present a way to utilize Wf/W composites for divertor applications by two main fabrication routes based on the chemical vapor deposition (CVD) of tungsten and powder metallurgy. A new device dedicated to the chemical deposition of W enhances significantly the available machine time for processing and optimization. Modeling shows that good deposition results are achievable by the use of a convectional flow and a directed temperature profile in an infiltration process. Recent developments in the area of multi-fiber powder-metallurgical Wf/W mark a possible path towards a component based on standard tungsten production technologies. Field Assisted Sintering Technology (FAST) is used as production route to achieve 94 % dense materials. Initial mechanical tests and micro-structural analyses show potential for pseudo-ductile behavior of materials with a reasonable (30 %) fiber fraction. In the as-fabricated condition samples showed step-wise cracking while the material is still able to bear rising load, the typical pseudo-ductile behavior of a composite. Yttria is used as the interface material in order to allow the energy dissipation mechanisms required. The use of Wf/W could broaden the operation temperature window of tungsten significantly and mitigate problems of deep cracking occurring typically in cyclic high heat flux loading. Furthermore, Wf/W can potentially bridge the operational gap between the upper bound for strength of copper ∼ 620 K and the lower bound of DBTT for tungsten ∼ 850 K.

J. W. Coenen

Papers

Power Handling of the Tungsten Divertor in JET

Powder metallurgically produced tungsten fiber-reinforced tungsten composites

Second plasma exposure of a pre-damaged ITER-like Plasma Facing Unit in the WEST tokamak: in-situ and post-mortem measurements

Tungsten Composite Materials for Fusion First Wall Applications

Advanced Materials for a Damage Resilient Divertor for DEMO